This invention is related to a photosensitive resin composition containing, as a catalyst precursor, a catalytic metal element with a metal-deposition catalytic activity suitable for electroless metal plating. In particular, this invention is related to a resin pattern with a metal-deposition catalytic activity suitable for electroless metal plating and to a method for the formation of the resin pattern. This invention is further related to a metal-resin composite prepared through an electroless metal plating treatment on the resin pattern with a metal-deposition catalytic activity suitable for electroless metal plating described above and a method for the formation of the metal-resin composite.
Currently, electroless metal plating treatment is used to form a conductive coating film on an insulating object. The electroless metal plating treatment is carried out through a procedure consisting of the following steps. A conditioning step is carried out using various surfactants to clean the surface and make the surface carry charges. A catalyst-coating step is carried out using a tin/palladium colloid bath. An activation step is carried out using hydrofluoric acid, etc., to activate the catalyst colloid adsorbed on the surface. Electroless metal plating is carried out using a plating bath containing a reducing agent, such as formalin, etc. When the substrate for the electroless metal plating treatment is a printed circuit board for example, carrying a pattern, the pattern can be formed with various methods, such as, but not limited to, the subtractive method, semiadditive method, and full-additive method.
Other methods, such as primer treatment using palladium or silver catalyst, etc., may also be used. In the primer treatment, a metal catalyst is introduced into a resin material containing solvent and inorganic filler. The resin material is coated onto a substrate to form a resin film containing a catalyst. Then, electroless metal plating is carried out to form a conductive film. The primer treatment is mainly used on a plastic surface for the purpose of electromagnetic interference (EMI) shielding.
In the semiconductor field, sputtering and chemical vapor deposition (CVD) are more commonly used for the formation of a conductive layer and the manufacturing technology has been established.
Moreover, a technology of introducing an organic metal salt, etc. with catalytic activity into a resin material and then forming a conducting film with the resin material is disclosed in U.S. Pat. No. 5,059,242 and has been used in the process of electrode formation.
In the current electroless metal plating process, the insulating resin material in the printed circuit board and semiconductor device is first treated with dry etching or using an agent, such as permanganic acid, etc., to generate a rough surface and improve wettability. Then, electroless copper plating or electroless nickel plating is conducted to form a conducting layer on the surface of the resin material.
However, it is very difficult to introduce a carboxyl group or a hydroxyl group to the resin matrix of a highly reliable insulating resin material. In fact, the carboxyl group or hydroxyl group may reduce the reliability of insulating resin material. As a result, the conducting layer formed through electroless metal plating has low adhesion strength to the surface of the insulating resin material. Moreover, for the materials not suitable for generating these anchoring groups, such as glass, ceramic, etc., to improve the attachment of a metal conductive layer, the metal conductive layer formed through electroless metal plating will also have low adhesive strength to the surface. The current electroless metal plating process consists of a series of complicated steps, including conditioning step, catalyst-coating step, activation step, and electroless metal plating step. In order to achieve stable production of high-quality products, it is necessary to have constant monitoring and management of all agents used in each step.
In the process of forming a conductive layer on a base material, currently the surface of the base material is first treated with oxygen plasma and then the conductive layer is formed with sputtering. Moreover, a conductive layer with the required thickness that can be formed by this method by further electrolytic metal plating. However, although sputtering is a standard method for the formation of a thin layer, the process of sputtering usually takes a long period of time and the metal target is expensive. Therefore, the cost of the sputtering process is relatively high.
On the other hand, the method for the formation of a conductive layer with an organic metal salt uses a resinate compound of palladium, silver, platinum, etc. The compound is dissolved in water or an organic solvent and the substrate to be coated is dipped into the solution to form a coating layer of the resinate compound. Then, thermal decomposition of the resinate compound generates a metal thin layer on the substrate to be coated. Finally, electroless or electrolytic metal plating is carried out to form a conductive layer. By using this method, however, the metal coating layer obtained has poor uniformity. In fact, the metal powder is simply attached to the surface of the substrate to be coated and the attachment is not very strong. In order to solve the problem, a paste is prepared by introducing the metal resinate into a synthetic resin material, which is then coated on the substrate to form a uniform coating layer. The paste is widely used to fill holes on printed circuit boards and form electrodes on LCD through screen printing.
However, the conducting paste is not suitable for semiconductors and semiconductor packages as well as other purposes requiring a high reliability. Moreover, it is very difficult to form fine lines through screen printing of the paste. In other words, when using an organic metal salt in the formation of electronic devices, a paste is first prepared by introducing an organic metal salt to a synthetic resin material and then coated on a substrate through screen printing, followed by sintering to convert the organic metal salt to the corresponding metal. In this process, the sintering temperature must be higher than the thermal decomposition temperature of the organic metal salt (at least 300° C.) to remove the synthetic resin material. Therefore, when the synthetic resin material is completely removed, only the metal pattern remains. However, when the method is used in the formation of semiconductor packages, since the base body of semiconductor packages is made of a composite material of epoxy resin reinforced with glass fiber, the high temperature used in the sintering step will cause thermal damage, such as deformation, cracks, etc., on the base body. In addition, since the synthetic resin material is completely removed in the sintering step, various defects, such as pinholes, wire breakage, etc., may be generated in the metal pattern obtained after sintering. In order to avoid these problems, a paste with a high metal content can be used. More specifically, when using a paste containing a gold resinate to form a gold wire, the gold content in the paste must be as high as 25 weight % and the sintering temperature is about 500° C. In other words, the sintering step in the current coating method will cause severe damage to the substrate to be coated. In order to form a metal pattern with a high reliability, the content of the expensive metal in the paste must be increased significantly, resulting in high production costs.